/*#include<stdio.h>
int main()
{
	long r;
	scanf("%ld",&r);
	double s;
	s=r*r*3.141592653;
	double z;
	z=s*10000000;
	z=(long)z%1000000;
	if(z>=5)
	s=s+0.0000001;
	printf("%.7lf",s);
	return 0;
}*/
#include <stdio.h>
#include <math.h>

int main() 
{
    int r;
    double area;
    const double PI = atan(1.0) * 4;

    scanf("%d", &r);
    area = PI * r * r;
    printf("%.7f\n", area);

    return 0;
}
